Recent research has shown that unborn babies (fetuses) have the ability to hear sound while still in the womb. An unborn baby may also recognize and react to certain sounds such as music, the mother's and/or father's voice, and a variety of other natural and/or man-made sounds. More specifically, research has indicated that fetus hearing ability begins to develop at approximately 16 to 18 weeks. Sensitivity to a broad range of frequencies in the audible range (from 20 Hz to 20000 Hz) progressively improves throughout the pregnancy. The playing of sounds and music to fetuses may have a variety of beneficial effects including: intellectual or cognitive development, stimulation, relaxation, parent child bonding and helping to turn babies who are breech into the correct position before birth. Newborn infants continue to respond to music played to them while in the womb. A familiar piece of music may have a calming effect after birth.